Robots capable of climbing vertical surfaces would be useful for disaster relief, surveillance, and maintenance applications. Various robots have used suction and magnets for climbing smooth surfaces. A controlled vortex that creates negative aerodynamic lift has also been demonstrated. However, these solutions require substantial power and generate noise even when stationary. Microspines, drawing inspiration from insects and spiders, have been used to climb rough surfaces such as brick and concrete.
For climbing on a range of vertical surfaces from smooth glass to rough stucco, various animals including insects, spiders, tree frogs and geckos employ wet or dry adhesion. The impressive climbing performance of these creatures has lead to a number of robots that employ adhesives for climbing. Sticky adhesives have the disadvantage that they quickly become dirty and lose adhesion. Another disadvantage is that the adhesive requires relatively high forces for attachment and detachment. Some researchers have circumvented this problem by using spoke-wheel designs that allow the detachment forces at a receding point of contact to provide the necessary attachment force at the next.
To overcome the problems with sticky adhesives, there has been a trend toward developing dry adhesives, which generally have a higher elastic modulus than pressure sensitive adhesives (PSAs) and rely on van der Waals forces between arrays of microscopic features and the substrate for adhesion. These have been modeled on the adhesive properties of geckos. In other work, climbing robots have used elastomeric microstructured tape or elastomeric pads that attract dirt after repeated use but, in contrast to PSAs, can be cleaned with water and reused. As feature sizes grow smaller, increasingly stiff and hydrophobic materials can be used while still obtaining sufficient real areas of contact for van der Waals forces to provide useful levels of adhesion. The result is an adhesive that resists dirt accumulation.
Currently, no single solution generates high adhesion, attaches with low preload, is rugged, self-cleaning, and can be scaled to climbing robot applications. The present invention addresses these shortcomings and advances the art of climbing robots and its applications thereof. In particular, the present invention provides new design mechanisms that are essential for a legged robot to climb and maneuver on vertical surfaces using dry adhesion. These design mechanisms enable: (i) hierarchical compliance for conforming at centimeter, millimeter, and micrometer scales; (ii) 2) directional adhesives so that the robot can control adhesion by controlling shear; and (iii) distributed force control that works with compliance and anisotropy to achieve stability.